iscsi-target: Fix ImmediateData=Yes failure regression in >= v3.10

This patch addresses a regression bug within ImmediateData=Yes failure
handling that ends up triggering an OOPs within >= v3.10 iscsi-target
code.

The problem occurs when iscsit_process_scsi_cmd() does the call to
target_put_sess_cmd(), and once again in iscsit_get_immediate_data()
that is triggered during two different cases:

 - When iscsit_sequence_cmd() returns CMDSN_LOWER_THAN_EXP, for which
   the descriptor state will already have been set to ISTATE_REMOVE
   by iscsit_sequence_cmd(), and
 - When iscsi_cmd->sense_reason is set, for which iscsit_execute_cmd()
   will have already called transport_send_check_condition_and_sense()
   to queue the exception response.

It changes iscsit_process_scsi_cmd() to drop the early call, and makes
iscsit_get_immediate_data() call target_put_sess_cmd() from a single
location after dumping the immediate data for the failed command.

The regression was initially introduced in commit:

commit 561bf15892375597ee59d473a704a3e634c4f311
Author: Nicholas Bellinger <nab@linux-iscsi.org>
Date:   Wed Jul 3 03:58:58 2013 -0700

    iscsi-target: Fix iscsit_sequence_cmd reject handling for iser

Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -1086,7 +1086,6 @@ int iscsit_process_scsi_cmd(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
 		if (cmd->reject_reason)
 			return 0;
 
-		target_put_sess_cmd(conn->sess->se_sess, &cmd->se_cmd);
 		return 1;
 	}
 	/*
@@ -1124,14 +1123,10 @@ after_immediate_data:
 		 */
 		cmdsn_ret = iscsit_sequence_cmd(cmd->conn, cmd,
 					(unsigned char *)hdr, hdr->cmdsn);
-		if (cmdsn_ret == CMDSN_ERROR_CANNOT_RECOVER) {
+		if (cmdsn_ret == CMDSN_ERROR_CANNOT_RECOVER)
 			return -1;
-		} else if (cmdsn_ret == CMDSN_LOWER_THAN_EXP) {
-			target_put_sess_cmd(conn->sess->se_sess, &cmd->se_cmd);
-			return 0;
-		}
 
-		if (cmd->sense_reason) {
+		if (cmd->sense_reason || cmdsn_ret == CMDSN_LOWER_THAN_EXP) {
 			int rc;
 
 			rc = iscsit_dump_data_payload(cmd->conn,